Seedling leaf turning yellow

My seedlings largest leaf has turned yellow but the other leaves are still a rich green plz help
http://imageshack.us/a/img441/4180/imagefcdw.jpg

those baby leaves are supposed to die off after it reaches higher maturity....but it does seem a little early for it to be doing that.
don't feed any nutes to seedlings and make sure your at least 2 feet away from the light.

You're stretching, get your light closer and get a fan on THEM.
What is your temp at leaf height?
If you're a beginner, I would suggest separating those plants, in case you fuck one up, you don't end up losing both.
How often are you watering?
Have you fed? I hope not.

If you are using CFL lighting you want the bulbs as close as possible 2-4" is not too close if you have some air moving.

I do not use any nutes yet and I'm sure I don't over water them. I use one cfl since they're only seedlings and its about 6 inches away. The funny thing is that one is big and strong and the other is weak and sad looking http://imageshack.us/a/img823/8725/imagekzcl.jpg